Gas branching apparatus and method for manufacturing fine glass particle deposited body using the same

ABSTRACT

A gas branching apparatus that branches and supplies a gas to first to N-th supply targets, includes first to N-th pipes wherein the first to N-th pipes are each branched into first to N-th branch pipes on a downstream end side, and wherein the i-th branch pipes of the respective first to N-th pipes are connected in common to the i-th supply target, and the i-th branch pipes of the respective first to N-th pipes are provided with valves, respectively, where i denotes each of integers of 1 to N.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/621,446, filed Jun. 13, 2017, which is a continuation applicationof International Application No. PCT/JP2016/000053, filed Jan. 7, 2016,which claims the benefit of Japanese Patent Applications No.2015-002533, filed Jan. 8, 2015, No. 2015-002535, filed Jan. 8, 2015,and No. 2015-002538, filed Jan. 8, 2015. The contents of theaforementioned applications are incorporated herein by reference intheir entireties.

FIELD

The present invention relates to a gas branching apparatus that branchesand supplies a gas to a plurality of supply targets, and a method formanufacturing a fine glass particle deposited body using the same.

BACKGROUND

A quartz glass optical fiber is generally manufactured by forming anoptical fiber base material called a preform and drawing the preform. Inthe manufacturing of a preform, a fine glass particle deposited bodyformed of an aggregate of fine glass particles is dehydrated andsintered by heating. As methods for manufacturing the glass particledeposited body, a vapor-phase axial deposition (VAD) method, an outsidevapor deposition (OVD) method, and the like are known, for example.

In the OVD method, two or more burners are arranged around a long corematerial along a longitudinal direction of the core material, and a rawgas containing SiCl₄ and so on is supplied into oxyhydrogen flamesgenerated by the burners. Thus, fine glass particles are generated anddeposited on the core material to form a fine glass particle depositedbody. Thereafter, the fine glass particle deposited body is dehydratedand sintered in a furnace to obtain a preform.

Regarding the aforementioned method for manufacturing a fine glassparticle deposited body, Japanese Patent Application Laid-Open No. Hei3-279234 discloses that gas conditions of burners arranged at equalintervals across the overall length of a glass rod are individuallycontrolled such that the shape of the deposit can be equalized. Suchcontrol of the gas conditions of the respective burners uses mass flowcontrollers (MFCs) provided for the respective burners.

Moreover, Japanese Patent Application Laid-Open No. Hei 8-284904 andJapanese Patent Specification No. 5090646 describe the use of a flowdivider and the like to branch a gas flow into a plurality of partialgas flows, in order to ensure that the gas is fed to the burners withhigh uniformity and reproducibility.

As in the case of the method for manufacturing a fine glass particledeposited body for optical fiber, a plurality of supply targets such asburners arranged along a longitudinal direction of an object such as acore material manufacture a product while being supplied with a gas suchas a raw gas, a combustible gas, and a combustion-supporting gas, insome cases. In such a case, in order to ensure uniformity and stabilityof the manufactured product in the longitudinal direction, it isrequired to supply the gas with highest possible uniformity to theplurality of supply targets.

However, in the method using the MFCs provided for the respective supplytargets as described in Japanese Patent Application Laid-Open No. Hei3-279234, it is difficult to eliminate influences of aging changes inMFCs and of an individual difference among the MFCs.

Moreover, in the method using the flow divider as described in JapanesePatent Application Laid-Open No. Hei 8-284904 or Japanese PatentSpecification No. 5090646, influences of processing accuracy of the flowdivider itself are not negligible. Also, it is difficult to eliminate aresistance difference among pipes caused by an individual differenceamong the pipes. For this reason, even with the method using the flowdivider, it is difficult to perfectly equally branch the gas.

SUMMARY

The present invention is made in consideration of the above problems,and has an object to provide a gas branching apparatus capable ofsupplying a gas into a plurality of supply targets with high uniformity,and a method for manufacturing a fine glass particle deposited bodyusing the same.

According to one aspect of the present invention, there is provided agas branching apparatus that branches and supplies a gas to first toN-th supply targets (where N is an integer of 2 or more), including:first to N-th pipes, wherein the first to N-th pipes are each branchedinto first to N-th branch pipes on a downstream end side, and whereinthe i-th branch pipes of the respective first to N-th pipes areconnected in common to the i-th supply target, and the i-th branch pipesof the respective first to N-th pipes are provided with respectivevalves, where i denotes each of integers of 1 to N.

According to another aspect of the present invention, there is provideda gas branching apparatus that branches and supplies a gas to first toN-th supply targets (where N is an integer of 2 or more), including: aplurality of flow dividers each including first to N-th gas outletsthrough which the gas is branched and discharged; and a plurality ofpipes connecting one of the first to N-th gas outlets of each of theplurality of flow dividers to any of the first to N-th supply targets ona one-to-one basis, wherein the first to N-th gas outlets of each of theplurality of flow dividers are located at different positions in theflow divider, and wherein the plurality of gas outlets connected to thefirst to N-th supply targets, respectively, are located at the differentpositions in the flow dividers each other.

According to still another aspect of the present invention, there isprovided a gas branching apparatus that branches and supplies a gas tofirst to N-th (where N is an integer of 2 or more) supply targets,including: a plurality of flow dividers each including first to N-th gasoutlets through which the gas is branched and discharged, the flowdividers having different volumes; and a plurality of pipes connectingone of the first to N-th gas outlets of each of the plurality of flowdividers to any of the first to N-th supply targets on a one-to-onebasis.

According to still another aspect of the present invention, there isprovided a gas branching apparatus that branches and supplies a gas tofirst to N-th (where N is an integer of 2 or more) supply targets,including: a volume-variable flow divider including first to N-th gasoutlets through which the gas is branched and discharged; and aplurality of pipes connecting one of the first to N-th gas outlets ofthe flow divider to any of the first to N-th supply targets on aone-to-one basis.

According to the present invention, a gas can be supplied to a pluralityof supply targets with high uniformity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a gas branching apparatusaccording to a first embodiment of the present invention.

FIG. 2 is a flowchart showing operations of the gas branching apparatusaccording to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a gas branching apparatusaccording to a third embodiment of the present invention.

FIG. 4 is a flowchart showing operations of the gas branching apparatusaccording to the third embodiment of the present invention.

FIG. 5 is a schematic diagram showing a gas branching apparatusaccording to a sixth embodiment of the present invention.

FIG. 6 is a flowchart showing operations of the gas branching apparatusaccording to the sixth embodiment of the present invention.

FIG. 7 is a schematic diagram showing a gas branching apparatusaccording to a seventh embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

With reference to FIGS. 1 and 2, description is given of a gas branchingapparatus according to a first embodiment of the present invention. FIG.1 is a schematic diagram showing the gas branching apparatus accordingto this embodiment. FIG. 2 is a flowchart showing operations of the gasbranching apparatus according to this embodiment.

First, with reference to FIG. 1, description is given of a configurationof the gas branching apparatus according to this embodiment.

As shown in FIG. 1, the gas branching apparatus 100 according to thisembodiment branches and supplies a gas into a plurality of burners 10-1to 10-5, which are supply targets to be supplied with the gas. Note thatthe following description is given of, as an example, the case where theburners 10-1 to 10-5 are burners for manufacturing a fine glass particledeposited body for optical fiber by use of the OVD method. Also, whilethe number of the burners is not particularly limited as long as two ormore burners are provided, the following description is given of, as anexample, the case where five burners 10-1 to 10-5 are used.

The burners 10-1 to 10-5 are made of quartz glass, for example, whichare manufactured with the same design. Each of the burners 10-1 to 10-5is supplied with a plurality of gases to form a flame and introduce araw gas into the flame. The plurality of gases to be supplied to each ofthe burners 10-1 to 10-5 are, for example, hydrogen (H₂) gas, oxygen(O₂) gas, argon (Ar) gas, and raw gas. The raw gas includes SiCl₄ andthe like. In the OVD method, for each of the burners 10-1 to 10-5, suchgases are used to form an oxyhydrogen flame and the raw gas isintroduced into the oxyhydrogen flame. Although flow rates of therespective gases to the burners 10-1 to 10-5 are not particularlylimited, a flow rate of the H₂ gas is, for example, 20000 to 40000 sccm.A flow rate of the O₂ gas is, for example, 35000 to 40000 sccm. A flowrate of the Ar gas is, for example, 3000 to 5000 sccm. A flow rate ofthe raw gas is, for example, 3000 to 10000 sccm.

Note that the following description is given of, as an example, aconfiguration where one of the plurality of gases is supplied to each ofthe burners 10-1 to 10-5. However, a configuration where another gas issupplied to each of the burners 10-1 to 10-5 may also be the same as theconfiguration described below.

A long rod-shaped core material 12, onto which flames are blown from theburners 10-1 to 10-5, is a material on which fine glass particles aredeposited to be a preform, and is a glass rod, for example. The corematerial 12 is held such that its longitudinal direction is horizontal.Also, the core material 12 is held so as to be rotatable with itscentral axis as a rotation axis. The length of the core material 12 is,for example, but not particularly limited to, several meters, morespecifically, 1 to 2 m, for example.

The burners 10-1 to 10-5 are arranged in the horizontal direction atequal intervals along the longitudinal direction of the long rod-shapedcore material 12. Note that while the description is given of, as anexample, the case where the five burners 10-1 to 10-5 are provided inthis embodiment, the number of burners to be arranged for the corematerial 12 having a length of 1 to 2 m, for example, can be set to 5 to30. Thus, since the burners 10-1 to 10-5 are arranged at equalintervals, a plurality of flames from the burners 10-1 to 10-5 are blowntoward the core material 12 at equal intervals.

Moreover, the burners 10-1 to 10-5 are configured to be movable back andforth within a predetermined range along the longitudinal direction ofthe core material 12. Note that the core material 12 may be configuredto be movable back and forth along its longitudinal direction, insteadof the burners 10-1 to 10-5 being configured to be movable back andforth.

The gas branching apparatus 100 according to this embodiment includes aflow divider 14 configured to branch a gas to be supplied to theplurality of burners 10-1 to 10-5. Also, the gas branching apparatus 100according to this embodiment includes a piping system for supplying agas to the flow divider 14 and a piping system for connecting betweenthe flow divider 14 and the plurality of burners 10-1 to 10-5.

The flow divider 14 is made of metal, for example, and includes two gasinlets 14 i-1 and 14 i-2 and a plurality of gas outlets 14 o-1 to 14o-5, which are the same in number as the plurality of burners 10-1 to10-5. The plurality of gas outlets 14 o-1 to 14 o-5 are provided atequal intervals in a certain array direction. The flow divider 14 isdisposed such that the array direction of the plurality of gas outlets14 o-1 to 14 o-5 is horizontal as in the case of the longitudinaldirection of the core material 12, for example.

Note that the volume of the flow divider 14 is, for example, but notparticularly limited to, 1000 to 5000 cm³, which can be selectedaccording to gas supply conditions and the like. Moreover, while thedescription is given of the case where the flow divider 14 includes thetwo gas inlets 14 i-1 and 14 i-2, the number of the gas inlets is notlimited to 2. The number of the gas inlets may be one or two or more,and can be changed as needed according to the volume of the flow divider14, and the like.

The gas branching apparatus 100 according to this embodiment includespipes 16-1 and 16-2 for supplying the flow divider 14 with the same kindof gas as that to be supplied to the burners 10-1 to 10-5. The pipes16-1 and 16-2 have their upstream ends connected to a supply source (notshown) of the gas to be supplied to the burners 10-1 to 10-5. The pipes16-1 and 16-2 are provided with MFCs 18-1 and 18-2, respectively. TheMFCs 18-1 and 18-2 enable control of flow rates of gases flowing towardthe flow divider 14 through the pipes 16-1 and 16-2.

The pipes 16-1 and 16-2 have their downstream ends connected to the twogas inlets 14 i-1 and 14 i-2 of the flow divider 14, respectively.

Moreover, the flow divider 14 is disposed upstream of a plurality ofpipes 20-1 to 20-5. The pipes 20-1 to 20-5 have their upstream endsconnected to the plurality of gas outlets 14 o-1 to 14 o-5 of the flowdivider 14, respectively. The flow divider 14 is designed so as to havean equal branching ratio of the gas to the plurality of gas outlets 14o-1 to 14 o-5. More specifically, the flow divider 14 is designed suchthat the gas introduced into the flow divider 14 through the pipes 16-1and 16-2 is delivered into the pipes 20-1 to 20-5 with an equalbranching ratio through the plurality of gas outlets 14 o-1 to 14 o-5.

The pipes 20-1 to 20-5 are each branched, at their downstream end side,into a plurality of branch pipes, which are the same in number as theplurality of burners 10-1 to 10-5. More specifically, the pipe 20-1 isbranched into branch pipes 20-1-1 to 20-1-5 at its downstream end side.The pipe 20-2 is branched into branch pipes 20-2-1 to 20-2-5 at itsdownstream end side. The pipe 20-3 is branched into branch pipes 20-3-1to 20-3-5 at its downstream end side. The pipe 20-4 is branched intobranch pipes 20-4-1 to 20-4-5 at its downstream end side. The pipe 20-5is branched into branch pipes 20-5-1 to 20-5-5 at its downstream endside.

The branch pipes of the pipes 20-1 to 20-5 are provided with air valvesfor opening and closing the branch pipes, respectively. Morespecifically, the branch pipes 20-1-1 to 20-1-5 are provided with airvalves AV11, AV12, AV13, AV14, and AV15, respectively. The branch pipes20-2-1 to 20-2-5 are provided with air valves AV21, AV22, AV23, AV24,and AV25, respectively. The branch pipes 20-3-1 to 20-3-5 are providedwith air valves AV31, AV32, AV33, AV34, and AV35, respectively. Thebranch pipes 20-4-1 to 20-4-5 are provided with air valves AV41, AV42,AV43, AV44, and AV45, respectively. The branch pipes 20-5-1 to 20-5-5are provided with air valves AV51, AV52, AV53, AV54, and AV55,respectively. Note that, in the following description, these air valvesmay be described as the air valves AVxy (where x is an integer thatsatisfies 1≤x≤5 and y is an integer that satisfies 1≤y≤5).

The branch pipes 20-1-1, 20-2-1, 20-3-1, 20-4-1, and 20-5-1, which arebranched from different pipes from each other, have their downstreamends connected in common to an upstream end of a pipe 22-1. The branchpipes 20-1-2, 20-2-2, 20-3-2, 20-4-2, and 20-5-2, which are branchedfrom different pipes from each other, have their downstream endsconnected in common to an upstream end of a pipe 22-2. The branch pipes20-1-3, 20-2-3, 20-3-3, 20-4-3, and 20-5-3, which are branched fromdifferent pipes from each other, have their downstream ends connected incommon to an upstream end of a pipe 22-3. The branch pipes 20-1-4,20-2-4, 20-3-4, 20-4-4, and 20-5-4, which are branched from differentpipes from each other, have their downstream ends connected in common toan upstream end of a pipe 22-4. The branch pipes 20-1-5, 20-2-5, 20-3-5,20-4-5, and 20-5-5, which are branched from different pipes from eachother, have their downstream ends connected in common to an upstream endof a pipe 22-5.

The pipe 22-1 has its downstream end connected to the burner 10-1, sothat the burner 10-1 is supplied with a gas through the pipe 22-1. Thepipe 22-2 has its downstream end connected to the burner 10-2, so thatthe burner 10-2 is supplied with a gas through the pipe 22-2. The pipe22-3 has its downstream end connected to the burner 10-3, so that theburner 10-3 is supplied with a gas through the pipe 22-3. The pipe 22-4has its downstream end connected to the burner 10-4, so that the burner10-4 is supplied with a gas through the pipe 22-4. The pipe 22-5 has itsdownstream end connected to the burner 10-5, so that the burner 10-5 issupplied with a gas through the pipe 22-5.

The gas branching apparatus 100 according to this embodiment furtherincludes a controller 24 configured to control opening and closing ofthe air valves AVxy. The controller 24 includes a CPU (not shown)configured to execute various kinds of processing such as calculation,control, and determination. The controller 24 also includes a ROM (notshown) configured to store various control programs to be executed bythe CPU, a database to be referred to by the CPU, and the like. Thecontroller 24 further includes a RAM (not shown) configured totemporarily store data that is being processed by the CPU, input data,and the like.

The controller 24 controls opening and closing of the air valves AVxy soas to randomly switch between the opened and closed states of the airvalves AVxy two or more times during manufacturing of the preform usingthe flames from the burners 10-1 to 10-5. As to switching between theopened and closed states of the air valves AVxy, the controller 24controls opening and closing of the air valves AVxy so as to satisfy thefollowing conditions (I) and (II).

(I) for x=1 to 5, one of the air valves AVx1, AVx2, AVx3, AVx4, and AVx5is set to the opened state, and the rest are set to the closed state.

(II) for y=1 to 5, one of the air valves AV1 y, AV2 y, AV3 y, AV4 y, andAV5 y is set to the opened state, and the rest are set to the closedstate.

The controller 24 executes such switching between the opened and closedstates of the air valves AVxy at predetermined time intervals. This timeinterval can be, but not particularly limited to, 1 to 10 minutes, forexample.

During manufacturing of the fine glass particle deposited body, theswitching between the opened and closed states of the air valves AVxy bythe controller 24 described above allows the plurality of gas outlets 14o-1 to 14 o-5 of the flow divider 14 to be connected to the plurality ofburners 10-1 to 10-5 on a one-to-one basis. Furthermore, the gas outlets14 o-1 to 14 o-5 of the flow divider 14 to be connected to the burners10-1 to 10-5 are randomly switched.

In the gas branching apparatus 100 according to this embodiment, theflow divider 14 is designed so as to have an equal branching ratio ofthe gas to the plurality of gas outlets 14 o-1 to 14 o-5. Also, thepipes are designed so as to minimize a difference in pipe resistancefrom the plurality of gas outlets 14 o-1 to 14 o-5 to the burners 10-1to 10-5. However, processing accuracy or aging changes may cause thebranching ratio of the flow divider 14 to be not completely even.Moreover, processing accuracy or aging changes may cause a difference inpipe resistance from the plurality of gas outlets 14 o-1 to 14 o-5 tothe burners 10-1 to 10-5. Furthermore, even though the burners 10-1 to10-5 are manufactured with the same design, there is an individualdifference thereamong due to the processing accuracy or aging changes.Thus, there are variations in members or parts due to the processingaccuracy or aging changes, between the flow divider 14 and the burners10-1 to 10-5. Such variations in members or parts make it difficult tosupply the gas to the plurality of burners 10-1 to 10-5 with highuniformity. As a result, uniformity and stability of the fine glassparticle deposited body in its longitudinal direction, which ismanufactured along the longitudinal direction of the core material 12,may be impaired.

To counter this, in the gas branching apparatus 100 according to thisembodiment, the switching between the opened and closed states of theair valves AVxy by the controller 24 randomly switches the gas outlets14 o-1 to 14 o-5 of the flow divider 14 connected to the burners 10-1 to10-5. Thus, such influences of the variations in members or parts due tothe processing accuracy or aging changes as described above are canceledout. Accordingly, the influences of the variations in members or partscan be reduced. Therefore, according to this embodiment, the gas can besupplied to the plurality of burners 10-1 to 10-5 with high uniformitywhile reducing the influences of the variations in members or parts.This way, according to this embodiment, a fine glass particle depositedbody excellent in uniformity and stability in the longitudinal directioncan be manufactured. Moreover, even in the event of replacement ofburners or pipes, the same gas supply state as that before thereplacement can be reproduced with high reproducibility. Thus, a fineglass particle deposited body excellent in uniformity and stability inthe longitudinal direction can be manufactured with highreproducibility.

Next, with reference to FIG. 2, description is further given ofoperations of the gas branching apparatus 100 according to thisembodiment.

Before the gas branching apparatus 100 starts its operation, the airvalves AVxy are all set in the closed state.

First, the gas branching apparatus 100 starts its operation, therebyintroducing a gas into the flow divider 14 through the pipes 16-1 and16-2. During the introduction of the gas through the pipes 16-1 and16-2, the MFCs 18-1 and 18-2 control the flow rates of the gases flowingthrough the pipes 16-1 and 16-2, respectively.

Next, the controller 24 controls opening and closing of the air valvesAVxy (Step S11). Thus, the opened and closed states of the air valvesAVxy are set to those that satisfy the above conditions (I) and (II). Asfor the control of opening and closing of the air valves AVxy, thecontroller 24 generates a random number or pseudo random number, forexample, to select the air valve to be set to the opened state based onthe generated random number or pseudo random number. Then, thecontroller 24 sets the selected air valve in the opened state and therest in the closed state.

After setting the opened and closed states of the air valves AVxy asdescribed above, gases are supplied to the plurality of burners 10-1 to10-5, respectively (Step S12). Also, other gases used to manufacture afine glass particle deposited body are similarly supplied to theplurality of burners 10-1 to 10-5.

In the respective burners 10-1 to 10-5 supplied with the gases asdescribed above, flames are formed using a fuel gas among the gasessupplied, and a raw gas among the gases supplied is introduced into theflames. Thus, the flames containing the raw material are blown onto thecore material 12 rotated with its central axis as a rotation axis.Accordingly, fine glass particles to be a preform of optical fiber aresequentially deposited on the core material 12. Note that, in themeantime, the plurality of burners 10-1 to 10-5 may be moved back andforth along the longitudinal direction of the core material 12.

During the deposition of the fine glass particles on the core material12 as described above, the deposition weight of the fine glass particlesdeposited on the core material 12 is monitored, and it is determinedbased on the monitored deposition weight whether or not to terminate thedeposition of the fine glass particles (Step S13).

When the deposition weight of the fine glass particles is less than apredetermined weight and the deposition is continued rather than beingterminated (Step S13, NO), it is determined whether or not a timeinterval for switching between the opened and closed states of the airvalves AVxy has passed (Step S14).

When the time interval for switching between the opened and closedstates of the air valves AVxy has not passed (Step S14, NO), theprocessing returns to Step S12 to continue the deposition of the fineglass particles while supplying the respective gases.

On the other hand, when the time interval for switching between theopened and closed states of the air valves AVxy has passed (Step S14,YES), the processing returns to Step S11 to again control opening andclosing of the air valves AVxy by the controller 24. Thus, afterrandomly switching the opened and closed states of the air valves AVxyto those that satisfy the above conditions (I) and (II), the depositionof the fine glass particles is continued while supplying the respectivegases. As for the control of opening and closing of the air valves AVxy,the controller 24 generates a random number or pseudo random number, forexample, to select the air valve to be set to the opened state based onthe generated random number or pseudo random number. Then, thecontroller 24 sets the selected air valve in the opened state and therest in the closed state.

As described above, according to this embodiment, the random switchingbetween the opened and closed states of the air valves AVxy by thecontroller 24 randomly switches the gas outlets 14 o-1 to 14 o-5 of theflow divider 14 connected to the burners 10-1 to 10-5. Thus, influencesof variations in members or parts due to processing accuracy or agingchanges can be reduced.

Note that it is preferable that the switching between the opened andclosed states of the air valves AVxy is performed such that a cumulativetime of times when the gases from the gas outlets 14 o-1 to 14 o-5 aresupplied to the respective burners 10-1 to 10-5 is equal among theburners 10-1 to 10-5. Thus, the influences of the variations in membersor parts due to processing accuracy or aging changes can be furtherreduced. As a result, the gases can be supplied to the plurality ofburners 10-1 to 10-5 with higher uniformity.

On the other hand, when the deposition weight of the fine glassparticles is the predetermined weight and thus the deposition is to beterminated (Step S13, YES), the controller 24 sets all the air valvesAVxy in the closed state (Step S15). Thus, the deposition of the fineglass particles on the core material 12 is terminated to obtain a fineglass particle deposited body that is a deposition of the fine glassparticles.

Thereafter, the fine glass particle deposited body thus obtained isdehydrated and sintered in a furnace to obtain a preform.

As described above, according to this embodiment, gases can be suppliedto a plurality of supply targets with high uniformity.

Second Embodiment

A gas branching apparatus according to a second embodiment of thepresent invention is described. Note that the same constituentcomponents as those in the gas branching apparatus according to thefirst embodiment described above are denoted by the same referencenumerals, and description thereof is omitted or simplified.

In the first embodiment described above, the description is given of, asan example, the case where the opening and closing of the air valvesAVxy are controlled so as to randomly switch between the opened andclosed states of the air valves AVxy two or more times. However, thecontrol of the opening and closing of the air valves AVxy is not limitedto the case where the control is performed so as to randomly switchbetween the opened and closed states of the air valves AVxy two or moretimes. For example, the opening and closing of the air valves AVxy maybe controlled so as to regularly switch between the opened and closedstates of the air valves AVxy two or more times.

In this embodiment, description is given of the case where opening andclosing of the air valves AVxy are controlled so as to regularly switchbetween the opened and closed states of the air valves AVxy two or moretimes.

In this case, for example, every time a predetermined time interval forswitching between the opened and closed states of the air valves AVxypasses, opening and closing of the air valves AVxy in each of thefollowing valve groups are synchronized and controlled as describedbelow.

First, as for a valve group of the air valves AV11 to AV15, the airvalve AV11, the air valve AV12, the air valve AV13, the air valve AV14,and the air valve AV15 are sequentially and repeatedly set to the openedstate in this order. Meanwhile, the rest of the air valves other thanthe air valves set to the opened state are set to the closed state.

As for a valve group of the air valves AV21 to AV25, the air valve AV22,the air valve AV23, the air valve AV24, the air valve AV25, and the airvalve AV21 are sequentially and repeatedly set to the opened state inthis order. Meanwhile, the rest of the air valves other than the airvalves set to the opened state are set to the closed state.

As for a valve group of the air valves AV31 to AV35, the air valve AV33,the air valve AV34, the air valve AV35, the air valve AV31, and the airvalve AV32 are sequentially and repeatedly set to the opened state inthis order. Meanwhile, the rest of the air valves other than the airvalves set to the opened state are set to the closed state.

As for a valve group of the air valves AV41 to AV45, the air valve AV44,the air valve AV45, the air valve AV41, the air valve AV42, and the airvalve AV43 are sequentially and repeatedly set to the opened state inthis order. Meanwhile, the rest of the air valves other than the airvalves set to the opened state are set to the closed state.

As for a valve group of the air valves AV51 to AV55, the air valve AV55,the air valve AV51, the air valve AV52, the air valve AV53, and the airvalve AV54 are sequentially and repeatedly set to the opened state inthis order. Meanwhile, the rest of the air valves other than the airvalves set to the opened state are set to the closed state.

As described above, the opening and closing of the air valves AVxy canalso be controlled so as to regularly switch two or more times betweenthe opened and closed states of the air valves AVxy to those thatsatisfy the above conditions (I) and (II). Such regular switchingbetween the opened and closed states of the air valves AVxy regularlyswitches the gas outlets 14 o-1 to 14 o-5 of the flow divider 14connected to the burners 10-1 to 10-5. Thus, such regular switching canalso reduce influences of variations in members or parts due toprocessing accuracy or aging changes. Therefore, according to thisembodiment, the gases can be supplied to the plurality of burners 10-1to 10-5 with high uniformity while reducing the influences of thevariations in members or parts.

Note that, in this case, again, it is preferable that the switchingbetween the opened and closed states of the air valves AVxy is performedsuch that a cumulative time of times when the gases from the gas outlets14 o-1 to 14 o-5 are supplied to the respective burners 10-1 to 10-5 isequal among the burners 10-1 to 10-5.

The present invention is not limited to the first and second embodimentsdescribed above, but various modifications can be made thereto.

For example, in the first and second embodiments, the description isgiven of, as an example, the case where the gas is branched and suppliedinto the five burners 10-1 to 10-5. However, the number of the burnersis not particularly limited as long as two or more burners are provided.

When a gas is branched and supplied into first to N-th (where N is aninteger of 2 or more) burners, the flow divider includes first to N-thgas outlets through which the gas is discharged, and is designed so asto have an equal branching ratio of the gas to the first to N-th gasoutlets. Also, it is assumed that upstream ends of first to N-th pipesare connected to the first to N-th gas outlets, respectively. Moreover,the first to N-th pipes are each branched into first to N-th branchpipes at their downstream end side. Furthermore, the i-th branch pipesof the respective first to N-th pipes are connected in common to thei-th burner, and the i-th branch pipes of the respective first to N-thpipes are provided with valves, respectively, where i denotes each ofintegers of 1 to N.

When the gas is branched and supplied to the first to N-th burners, thecontroller may control opening and closing of the valves so as tosatisfy the following first and second conditions. More specifically,the first condition is that one of N valves provided on the first toN-th branch pipes of the j-th pipe is set to the opened state, and therest are set to the closed state, where j denotes each of integers of 1to N. The second condition is that one of N valves provided on the k-thbranch pipes of the respective first to N-th pipes is set to the openedstate, and the rest are set to the closed state, where k denotes each ofintegers of 1 to N.

Moreover, in the first and second embodiments, the description is givenof, as an example, the case where the burners 10-1 to 10-5 are used as aplurality of supply targets to be supplied with the gas. However, thesupply targets are not limited to the burners. The supply targets may bethose subjected to some kind of processing, such as manufacturing ofproducts and processing on processed products, using the supplied gas.

Moreover, in the first and second embodiments, the description is givenof, as an example, the case where the burners 10-1 to 10-5 as the supplytargets are arranged along the longitudinal direction of the corematerial 12 that is a long object. However, the plurality of supplytargets do not always have to be those arranged along the longitudinaldirection of the object.

Moreover, in the first and second embodiments, the description is givenof, as an example, the case using the air valves AVxy. However, insteadof the air valves, various valves can be used, whose opening and closingcan be controlled by the controller 24. For example, electromagneticvalves or the like can be used instead of the air valves.

Moreover, in the first and second embodiments, the description is givenof, as an example, the case where the core material 12 is held such thatthe longitudinal direction thereof is horizontal. However, the mode ofholding the core material 12 is not limited thereto. For example, thecore material 12 may be held such that the longitudinal directionthereof is vertical. In this case, the burners 10-1 to 10-5 can bearranged at equal intervals along the longitudinal direction of the corematerial 12 that is vertically disposed. Moreover, the flow divider 14may be disposed such that the array direction of the plurality of gasoutlets 14 o-1 to 14 o-5 is horizontal, as in the above case, or canalso be disposed such that the array direction of the plurality of gasoutlets 14 o-1 to 14 o-5 is vertical.

Moreover, the first and second embodiments are also applicable to thecase where no flow divider is used or where the branching ratio of theflow divider is not even.

Third Embodiment

With reference to FIGS. 3 and 4, description is given of a gas branchingapparatus according to a third embodiment of the present invention. FIG.3 is a schematic diagram showing the gas branching apparatus accordingto this embodiment. FIG. 4 is a flowchart showing operations of the gasbranching apparatus according to this embodiment.

First, with reference to FIG. 3, description is given of a configurationof the gas branching apparatus according to this embodiment.

As shown in FIG. 3, a gas branching apparatus 1100 according to thisembodiment branches and supplies a gas into a plurality of burners 110-1to 110-3, which are supply targets to be supplied with the gas. Notethat the following description is given of, as an example, the casewhere the burners 110-1 to 110-3 are burners for manufacturing a fineglass particle deposited body for optical fiber by use of the OVDmethod. Also, while the number of the burners is not particularlylimited as long as two or more burners are provided, the followingdescription is given of, as an example, the case where three burners110-1 to 110-3 are used.

The burners 110-1 to 110-3 are made of quartz glass, for example, whichare manufactured with the same design. Each of the burners 110-1 to110-3 is supplied with a plurality of gases to form a flame andintroduce a raw gas into the flame. The plurality of gases to besupplied to each of the burners 110-1 to 110-3 are, for example,hydrogen (H₂) gas, oxygen (O₂) gas, argon (Ar) gas, and raw gas. The rawgas includes SiCl₄ and the like. In the OVD method, for each of theburners 110-1 to 110-3, such gases are used to form an oxyhydrogen flameand the raw gas is introduced into the oxyhydrogen flame. Although flowrates of the respective gases to the burners 110-1 to 110-3 are notparticularly limited, a flow rate of the H₂ gas is, for example, 20000to 40000 sccm. A flow rate of the O₂ gas is, for example, 35000 to 40000sccm. A flow rate of the Ar gas is, for example, 3000 to 5000 sccm. Aflow rate of the raw gas is, for example, 3000 to 10000 sccm.

Note that the following description is given of, as an example, aconfiguration where one of the plurality of gases is supplied to each ofthe burners 110-1 to 110-3. However, a configuration where another gasis supplied to each of the burners 110-1 to 110-3 may also be the sameas the configuration described below.

A long rod-shaped core material 112, onto which flames are blown fromthe burners 110-1 to 110-3, is a material on which fine glass particlesare deposited to be a preform, and is a glass rod, for example. The corematerial 112 is held such that its longitudinal direction is vertical.Also, the core material 112 is held so as to be rotatable with itscentral axis as a rotation axis. The length of the core material 112 is,for example, but not particularly limited to, several meters, morespecifically, 1 to 2 m, for example.

When the core material 112 is increased in size and thus increased inlength or weight, deflection occurs in the core material 112 if the corematerial 112 is held such that the longitudinal direction thereof ishorizontal. This makes it difficult to manufacture a fine glass particledeposited body while ensuring uniformity in the longitudinal direction.In this embodiment, since the core material 112 is held such that thelongitudinal direction thereof is vertical, occurrence of deflection inthe core material 112 can be suppressed.

The burners 110-1 to 110-3 are arranged in the vertical direction atequal intervals along the longitudinal direction of the long rod-shapedcore material 112. Note that while the description is given of, as anexample, the case where the three burners 110-1 to 110-3 are provided inthis embodiment, the number of burners to be arranged for the corematerial 112 having a length of 1 to 2 m, for example, can be set to 5to 30. Thus, since the burners 110-1 to 110-3 are arranged at equalintervals, a plurality of flames from the burners 110-1 to 110-3 areblown toward the core material 112 at equal intervals.

Moreover, the burners 110-1 to 110-3 are configured to be movable backand forth within a predetermined range along the longitudinal directionof the core material 112. Note that the core material 112 may beconfigured to be movable back and forth along its longitudinaldirection, instead of the burners 110-1 to 110-3 being configured to bemovable back and forth.

The gas branching apparatus 1100 according to this embodiment includes aplurality of flow dividers 114-1 to 114-3 configured to branch a gas tobe supplied to the plurality of burners 110-1 to 110-3. Also, the gasbranching apparatus 1100 according to this embodiment includes a pipingsystem for supplying a gas to the flow dividers 114-1 to 114-3 and apiping system for connecting between the plurality of flow dividers114-1 to 114-3 and the plurality of burners 110-1 to 110-3.

The flow dividers 114-1 to 114-3 are made of metal, for example, andmanufactured with the same design.

The flow divider 114-1 includes two gas inlets 114-1 i-1 and 114-1 i-2and a plurality of gas outlets 114-1 o-1 to 114-1 o-3, which are thesame in number as the plurality of burners 110-1 to 110-3. The pluralityof gas outlets 114-1 o-1 to 114-1 o-3 are provided at equal intervals ina certain array direction.

The flow divider 114-2 includes two gas inlets 114-2 i-1 and 114-2 i-2and a plurality of gas outlets 114-2 o-1 to 114-2 o-3, which are thesame in number as the plurality of burners 110-1 to 110-3. The pluralityof gas outlets 114-2 o-1 to 114-2 o-3 are provided at equal intervals ina certain array direction.

The flow divider 114-3 includes two gas inlets 114-3 i-1 and 114-3 i-2and a plurality of gas outlets 114-3 o-1 to 114-3 o-3, which are thesame in number as the plurality of burners 110-1 to 110-3. The pluralityof gas outlets 114-3 o-1 to 114-3 o-3 are provided at equal intervals ina certain array direction.

The flow dividers 114-1 to 114-3 are vertically arranged in this orderfrom the upper side to the lower side. In the flow dividers 114-1 to114-3 vertically arranged, the array direction of the plurality of gasoutlets 114-1 o-1 to 114-1 o-3, 114-2 o-1 to 114-2 o-3, and 114-3 o-1 to114-3 o-3 is vertical as in the case of the longitudinal direction ofthe core material 112.

Since the flow dividers 114-1 to 114-3 are arranged as described above,the plurality of gas outlets of each of the flow dividers 114-1 to 114-3are located at different vertical positions, and thus have a differencein vertical level thereamong. More specifically, in the flow divider114-1, the gas outlet 114-1 o-1 is located in the upper level, the gasoutlet 114-1 o-2 is located in the middle level, and the gas outlet114-1 o-3 is located in the lower level. In the flow divider 114-2, thegas outlet 114-2 o-1 is located in the upper level, the gas outlet 114-2o-2 is located in the middle level, and the gas outlet 114-2 o-3 islocated in the lower level. In the flow divider 114-3, the gas outlet114-3 o-1 is located in the upper level, the gas outlet 114-3 o-2 islocated in the middle level, and the gas outlet 114-3 o-3 is located inthe lower level.

Note that the volume of the flow dividers 114-1 to 114-3 is, forexample, but not particularly limited to, 1000 to 5000 cm³, which can beselected according to gas supply conditions and the like. Moreover,while the description is given of the case where the flow dividers 114-1to 114-3 each include two gas inlets, the number of the gas inlets isnot limited to 2. The number of the gas inlets may be one or two ormore, and can be changed as needed according to the volume of the flowdividers 114-1 to 114-3, and the like.

The gas branching apparatus 1100 according to this embodiment includespipes 116-1 and 116-2 for supplying the flow dividers 114-1 to 114-3with the same kind of gas as that to be supplied to the burners 110-1 to110-3. The pipes 116-1 and 116-2 have their upstream ends connected to asupply source (not shown) of the gas to be supplied to the burners 110-1to 110-3. The pipes 116-1 and 116-2 are provided with MFCs 118-1 and118-2, respectively. The MFCs 118-1 and 118-2 enable control of flowrates of gases flowing toward the flow dividers 114-1 to 114-3 throughthe pipes 116-1 and 116-2.

The pipes 116-1 and 116-2 are each branched, at their downstream endside, into a plurality of branch pipes, which are the same in number asthe flow dividers 114-1 to 114-3. More specifically, the pipe 116-1 isbranched into branch pipes 116-1-1 to 116-1-3 at its downstream endside. The pipe 116-2 is branched into branch pipes 116-2-1 to 116-2-3 atits downstream end side.

The branch pipes 116-1-1 and 116-2-1 have their downstream endsconnected to two gas inlets 114-1 i-1 and 114-1 i-2 of the flow divider114-1, respectively. The branch pipes 116-1-2 and 116-2-2 have theirdownstream ends connected to two gas inlets 114-2 i-1 and 114-2 i-2 ofthe flow divider 114-2, respectively. The branch pipes 116-1-3 and116-2-3 have their downstream ends connected to two gas inlets 114-3 i-1and 114-3 i-2 of the flow divider 114-1, respectively.

The branch pipes of the pipes 116-1 and 116-2 are provided with airvalves for opening and closing the branch pipes, respectively. Morespecifically, the branch pipes 116-1-1 and 116-2-1 are provided with airvalves BV11 and BV12, respectively. The branch pipes 116-1-2 and 116-2-2are provided with air valves BV21 and BV22, respectively. The branchpipes 116-1-3 and 116-2-3 are provided with air valves BV31 and BV32,respectively. Note that, in the following description, these air valvesmay be described as the air valves BVxy (where x is an integer thatsatisfies 1≤x≤3 and y is 1 or 2).

Moreover, the pipes 120-1-1 to 120-1-3 have their upstream endsconnected to the plurality of gas outlets 114-1 o-1 to 114-1 o-3 of theflow divider 114-1, respectively. The flow divider 114-1 is designed soas to have an equal branching ratio of the gas to the plurality of gasoutlets 114-1 o-1 to 114-1 o-3. More specifically, the flow divider114-1 is designed such that the gas introduced into the flow divider114-1 through the pipes 116-1-1 and 116-2-1 is delivered into the pipes120-1-1 to 120-1-3 with an equal branching ratio through the pluralityof gas outlets 114-1 o-1 to 114-1 o-3.

The pipes 120-1-1 to 120-1-3 are provided with check valves CV11, CV12,and CV13, respectively. The check valves CV11, CV12, and CV13 preventthe gas in the pipes 120-1-1 to 120-1-3 from flowing back from thedownstream side toward the flow divider 114-1 that is the upstream side.Note that, instead of the check valves CV11, CV12, and CV13, air valvesmay be provided, which are opened and closed in synchronization with theair valves BV11 and BV12 on the gas inlet side.

Moreover, the pipes 120-2-1 to 120-2-3 have their upstream endsconnected to the plurality of gas outlets 114-2 o-1 to 114-2 o-3 of theflow divider 114-1, respectively. The flow divider 114-2 is designed soas to have an equal branching ratio of the gas to the plurality of gasoutlets 114-2 o-1 to 114-2 o-3. More specifically, the flow divider114-2 is designed such that the gas introduced into the flow divider114-2 through the pipes 116-1-2 and 116-2-2 is delivered into the pipes120-2-1 to 120-2-3 with an equal branching ratio through the pluralityof gas outlets 114-2 o-1 to 114-2 o-3.

The pipes 120-2-1 to 120-2-3 are provided with check valves CV21, CV22,and CV23, respectively. The check valves CV21, CV22, and CV23 preventthe gas in the pipes 120-2-1 to 120-2-3 from flowing back from thedownstream side toward the flow divider 114-2 that is the upstream side.Note that, instead of the check valves CV21, CV22, and CV23, air valvesmay be provided, which are opened and closed in synchronization with theair valves BV21 and BV22 on the gas inlet side.

Moreover, the pipes 120-3-1 to 120-3-3 have their upstream endsconnected to the plurality of gas outlets 114-3 o-1 to 114-3 o-3 of theflow divider 114-3, respectively. The flow divider 114-3 is designed soas to have an equal branching ratio of the gas to the plurality of gasoutlets 114-3 o-1 to 114-3 o-3. More specifically, the flow divider114-3 is designed such that the gas introduced into the flow divider114-3 through the pipes 116-1-3 and 116-2-3 is delivered into the pipes120-3-1 to 120-3-3 with an equal branching ratio through the pluralityof gas outlets 114-3 o-1 to 114-3 o-3.

The pipes 120-3-1 to 120-3-3 are provided with check valves CV31, CV32,and CV33, respectively. The check valves CV31, CV32, and CV33 preventthe gas in the pipes 120-3-1 to 120-3-3 from flowing back from thedownstream side toward the flow divider 114-3 that is the upstream side.Note that, instead of the check valves CV31, CV32, and CV33, air valvesmay be provided, which are opened and closed in synchronization with theair valves BV31 and BV32 on the gas inlet side.

Note that, in the following description, the above check valves may bedescribed as the check valves CVmn (where m is an integer that satisfies1≤m≤3 and n is an integer that satisfies 1≤n≤3).

The pipes 120-1-1, 120-2-2, and 120-3-3 have their downstream endsconnected in common to an upstream end of a pipe 122-1. These pipes120-1-1, 120-2-2, and 120-3-3 are connected to the gas outlets differentin vertical level in the flow dividers. More specifically, the pipe120-1-1 is connected to the gas outlet 114-1 o-1 in the upper level, thepipe 120-2-2 is connected to the gas outlet 114-2 o-2 in the middlelevel, and the pipe 120-3-3 is connected to the gas outlet 114-3 o-3 inthe lower level.

The pipes 120-1-3, 120-2-1, and 120-3-2 have their downstream endsconnected in common to an upstream end of a pipe 122-2. These pipes120-1-3, 120-2-1, and 120-3-2 are connected to the gas outlets differentin vertical level in the flow dividers. More specifically, the pipe120-1-3 is connected to the gas outlet 114-1 o-3 in the lower level, thepipe 120-2-1 is connected to the gas outlet 114-2 o-1 in the upperlevel, and the pipe 120-3-2 is connected to the gas outlet 114-3 o-2 inthe middle level.

The pipes 120-1-2, 120-2-3, and 120-3-1 have their downstream endsconnected in common to an upstream end of a pipe 122-3. These pipes120-1-2, 120-2-3, and 120-3-1 are connected to the gas outlets differentin vertical level in the flow dividers. More specifically, the pipe120-1-2 is connected to the gas outlet 114-1 o-2 in the middle level,the pipe 120-2-3 is connected to the gas outlet 114-2 o-3 in the lowerlevel, and the pipe 120-3-1 is connected to the gas outlet 114-3 o-1 inthe upper level.

The pipe 122-1 has its downstream end connected to the burner 110-1, sothat the burner 110-1 is supplied with a gas through the pipe 122-1. Thepipe 122-2 has its downstream end connected to the burner 110-2, so thatthe burner 110-2 is supplied with a gas through the pipe 122-2. The pipe122-3 has its downstream end connected to the burner 110-3, so that theburner 110-3 is supplied with a gas through the pipe 122-3.

Thus, the plurality of gas outlets of the plurality of flow dividers114-1 to 114-3 are connected in 1:1 through the pipes to any of theplurality of burners 110-1 to 110-3. More specifically, the gas outlet114-1 o-1 of the flow divider 114-1 is connected to the burner 110-1through the pipes 120-1-1 and 122-1. The gas outlet 114-1 o-2 of theflow divider 114-1 is connected to the burner 110-3 through the pipes120-1-2 and 122-3. The gas outlet 114-1 o-3 of the flow divider 114-1 isconnected to the burner 110-2 through the pipes 120-1-3 and 122-2. Thegas outlet 114-2 o-1 of the flow divider 114-2 is connected to theburner 110-2 through the pipes 120-2-1 and 122-2. The gas outlet 114-2o-2 of the flow divider 114-2 is connected to the burner 110-1 throughthe pipes 120-2-2 and 122-1. The gas outlet 114-2 o-3 of the flowdivider 114-2 is connected to the burner 110-3 through the pipes 120-2-3and 122-3. The gas outlet 114-3 o-1 of the flow divider 114-3 isconnected to the burner 110-3 through the pipes 120-3-1 and 122-3. Thegas outlet 114-3 o-2 of the flow divider 114-3 is connected to theburner 110-2 through the pipes 120-3-2 and 122-2. The gas outlet 114-3o-3 of the flow divider 114-3 is connected to the burner 110-1 throughthe pipes 120-3-3 and 122-1.

The gas branching apparatus 1100 according to this embodiment furtherincludes a controller 124 configured to control opening and closing ofthe air valves BVxy. The controller 124 includes a CPU (not shown)configured to execute various kinds of processing such as calculation,control, and determination. The controller 124 also includes a ROM (notshown) configured to store various control programs to be executed bythe CPU, a database to be referred to by the CPU, and the like. Thecontroller 124 further includes a RAM (not shown) configured totemporarily store data that is being processed by the CPU, input data,and the like.

The controller 124 controls opening and closing of the air valves BVxyso as to randomly switch two or more times the flow divider to be usedto branch the gas to any of the flow dividers 114-1 to 114-3 duringmanufacturing of the fine glass particle deposited body using the flamesfrom the burners 110-1 to 110-3. As to switching of the flow divider tobe used, the controller 124 controls opening and closing of the airvalves BV11 and BV12 in synchronization with the flow divider 114-1. Thecontroller 124 controls opening and closing of the air valves BV21 andBV22 in synchronization with the flow divider 114-2. The controller 124controls opening and closing of the air valves BV31 and BV32 insynchronization with the flow divider 114-3. Moreover, the controller124 sets any one of the pairs of the air valves to be controlled insynchronization, including the pair of the air valves BV11 and BV12, thepair of the air valves BV21 and BV22, and the pair of the air valvesBV31 and BV32, to the opened state, and the rest of the pairs to theclosed state.

The controller 124 executes such switching of the flow divider to beused at predetermined time intervals. This time interval can be, but notparticularly limited to, 1 to 10 minutes, for example.

During manufacturing of the fine glass particle deposited body, theswitching of the flow divider by the controller 124 described aboveallows any one of the flow dividers 114-1 to 114-3 to be used to branchthe gas to be supplied to the plurality of burners 110-1 to 110-3,thereby randomly switching the flow divider to be used.

When the flow divider to be used is changed, the vertical positions ofthe gas outlets of the flow divider for supplying the gas to theplurality of burners 110-1 to 110-3 are changed. More specifically, whenthe flow divider 114-1 is used, the gas is supplied to the burner 110-1through the upper gas outlet 114-1 o-1, to the burner 110-2 through thelower gas outlet 114-1 o-3, and to the burner 110-3 through the middlegas outlet 114-1 o-2. When the flow divider 114-2 is used, the gas issupplied to the burner 110-1 through the middle gas outlet 114-2 o-2, tothe burner 110-2 through the upper gas outlet 114-2 o-1, and to theburner 110-3 through the lower gas outlet 114-2 o-3. When the flowdivider 114-3 is used, the gas is supplied to the burner 110-1 throughthe lower gas outlet 114-3 o-3, to the burner 110-2 through the middlegas outlet 114-3 o-2, and to the burner 110-3 through the upper gasoutlet 114-3 o-1.

As for manufacturing of a fine glass particle deposited body, when thegas is branched by a flow divider and supplied to a plurality ofburners, an increase in size of the fine glass particle deposited bodyto be manufactured also increases the size of the flow divider itself,resulting in the need to increase the number of branches by the flowdivider. Moreover, when a core material is held such that itslongitudinal direction is horizontal, increases in weight of the corematerial and the fine glass particle deposited body cause deflectiontherein. In order to suppress such deflection, it is required to holdthe core material such that the longitudinal direction thereof isvertical. Moreover, in this case, in order to minimize pipe distancedifferences between the plurality of gas outlets of the flow divider andthe plurality of burners and pipe resistance differences associatedtherewith, it is also required to vertically arrange the flow dividersuch that the array direction of the plurality of gas outlets isvertical.

However, when the flow divider is vertically arranged as describedabove, the influence of gravity causes a pressure difference betweenvertical positions in the flow divider, which may result in a differencein branching ratio among the plurality of gas outlets. Particularly, agas having a relatively large specific gravity, such as the raw gas, islikely to be influenced by the gravity, and is thus likely to cause adifference in branching ratio. Such a difference in branching ratio ofthe flow divider makes it difficult to supply the gas to the pluralityof burners with high uniformity. As a result, uniformity and stabilityof the fine glass particle deposited body in its longitudinal direction,which is manufactured along the longitudinal direction of the corematerial, may be impaired.

To counter this, in the gas branching apparatus 1100 according to thisembodiment, the controller 124 randomly switches the flow divider to beused to branch the gas among the flow dividers 114-1 to 114-3. When theflow divider to be used is changed, the vertical positions of the gasoutlets of the flow divider for supplying the gas to the plurality ofburners 110-1 to 110-3 are changed as described above. Thus, suchinfluences of the gravity on branching of the gas by the flow divider asdescribed above due to the processing accuracy or aging changes asdescribed above are canceled out. Accordingly, the influences of thegravity can be reduced.

In the gas branching apparatus 1100 according to this embodiment, theplurality of flow dividers 114-1 to 114-3 are designed so as to have anequal branching ratio of the gas to the plurality of gas outlets. Also,the pipes are designed so as to minimize a difference in pipe resistancefrom the plurality of gas outlets to the burners 110-1 to 110-3.However, processing accuracy or aging changes may cause the branchingratio of the flow dividers 114-1 to 114-3 to be not completely even.Moreover, processing accuracy or aging changes may cause a difference inpipe resistance from the plurality of gas outlets to the burners 110-1to 110-3. Furthermore, even though the burners 110-1 to 110-3 aremanufactured with the same design, there is individual difference amongthe burners 110-1 to 110-3 due to the processing accuracy or agingchanges. Thus, there are variations in members or parts due to theprocessing accuracy or aging changes, between the flow dividers 114-1 to114-3 and the burners 110-1 to 110-3. Such variations in members orparts make it difficult to supply the gas to the plurality of burners110-1 to 110-3 with high uniformity. As a result, uniformity andstability of the fine glass particle deposited body in its longitudinaldirection, which is manufactured along the longitudinal direction of thecore material 112, may be impaired.

To counter this, in the gas branching apparatus 1100 according to thisembodiment, the controller 124 randomly switches the flow divider to beused to branch the gas as described above. Thus, such influences of thevariations in members or parts due to the processing accuracy or agingchanges as described above are canceled out. Accordingly, the influencesof the variations in members or parts can be reduced.

Therefore, according to this embodiment, the gas can be supplied to theplurality of burners 110-1 to 110-3 with high uniformity while reducingthe influences of the gravity and the influences of the variations inmembers or parts. This way, according to this embodiment, a fine glassparticle deposited body excellent in uniformity and stability in thelongitudinal direction can be manufactured. Moreover, even in the eventof replacement of burners or pipes, the same gas supply state as thatbefore the replacement can be reproduced with high reproducibility.Thus, a fine glass particle deposited body excellent in uniformity andstability in the longitudinal direction can be manufactured with highreproducibility.

Next, with reference to FIG. 4, description is further given ofoperations of the gas branching apparatus 1100 according to thisembodiment.

Before the gas branching apparatus 1100 starts its operation, the airvalves BVxy are all set in the closed state.

First, the gas branching apparatus 1100 starts its operation, therebyintroducing a gas into the flow dividers 114-1 to 114-3 through thepipes 116-1 and 116-2. During the introduction of the gas through thepipes 116-1 and 116-2, the MFCs 118-1 and 118-2 control the flow ratesof the gases flowing through the pipes 116-1 and 116-2, respectively.

Next, the controller 124 controls opening and closing of the air valvesBVxy. Thus, any one of the pairs of the air valves BV11 and BV12, BV21and BV22, and BV31 and BV32 is set to the opened state, and the rest ofthe pairs are set to the closed state. As for the control of opening andclosing of the air valves BVxy, the controller 124 generates a randomnumber or pseudo random number, for example, to select the pair of airvalves to be set to the opened state based on the generated randomnumber or pseudo random number. Then, the controller 124 sets theselected pair of air valves in the opened state and the rest in theclosed state. Thus, any one of the flow dividers 114-1 to 114-3 is setas the flow divider to be used to branch the gas (Step S111).

After setting the flow divider to be used to branch the gas as describedabove, the gas is branched by the set flow divider and supplied to theplurality of burners 110-1 to 110-3, respectively (Step S112). Note thatthe flow dividers 114-1 to 114-3 are provided with check valves CVmn onthe gas outlet side. Thus, no gas flows back into the flow divider thatis not used to branch the gas. Also, other gases used to manufacture afine glass particle deposited body are similarly supplied to theplurality of burners 110-1 to 110-3.

In the respective burners 110-1 to 110-3 supplied with the gases asdescribed above, flames are formed using a fuel gas among the gasessupplied, and a raw gas among the gases supplied is introduced into theflames. Thus, the flames containing the raw material are blown onto thecore material 112 rotated with its central axis as a rotation axis.Accordingly, fine glass particles to be a preform of optical fiber aresequentially deposited on the core material 112. Note that, in themeantime, the plurality of burners 110-1 to 110-3 may be moved back andforth along the longitudinal direction of the core material 112.

During the deposition of the fine glass particles on the core material112 as described above, the deposition weight of the fine glassparticles deposited on the core material 112 is monitored, and it isdetermined based on the monitored deposition weight whether or not toterminate the deposition of the fine glass particles (Step S113).

When the deposition weight of the fine glass particles is less than apredetermined weight and the deposition is continued rather than beingterminated (Step S113, NO), it is determined whether or not a timeinterval for switching the flow divider to be used to branch the gas haspassed (Step S114).

When the time interval for switching the flow divider to be used tobranch the gas has not passed (Step S114, NO), the processing returns toStep S112 to continue the deposition of the fine glass particles whilesupplying the respective gases.

On the other hand, when the time interval for switching the flow dividerto be used to branch the gas has passed (Step S114, YES), the processingreturns to Step S111 to again control opening and closing of the airvalves BVxy by the controller 124. Thus, any one of the pairs of the airvalves BV11 and BV12, BV21 and BV22, and BV31 and BV32 is set to theopened state, and the rest of the pairs are set to the closed state. Asfor the control of opening and closing of the air valves BVxy, thecontroller 124 generates a random number or pseudo random number, forexample, to select the pair of air valves to be set to the opened statebased on the generated random number or pseudo random number. Then, thecontroller 124 sets the selected pair of air valves in the opened stateand the rest in the closed state. Thus, the deposition of the fine glassparticles is continued while supplying the gases after randomlyswitching the flow divider to be used to branch the gas by setting theflow divider to be used to branch the gas again.

As described above, according to this embodiment, the random switchingof the flow divider by the controller 124 randomly switches the verticalpositions of the gas outlets of the flow divider connected to theburners 110-1 to 110-3. Thus, influences of gravity on the branchingration of the flow divider can be reduced. Moreover, influences ofvariations in members or parts due to processing accuracy or agingchanges can also be reduced.

Note that it is preferable that the switching of the flow divider to beused to branch the gas is performed such that a cumulative time of timeswhen the flow dividers 114-1 to 114-3 are used to branch the gas isequal thereamong. Thus, the influences of the gravity and the influencesof the variations in members or parts due to processing accuracy oraging changes can be further reduced. As a result, the gases can besupplied to the plurality of burners 110-1 to 110-3 with higheruniformity.

On the other hand, when the deposition weight of the fine glassparticles is the predetermined weight and thus the deposition is to beterminated (Step S113, YES), the controller 124 sets all the air valvesBVxy in the closed state (Step S115). Thus, the deposition of the fineglass particles on the core material 112 is terminated to obtain a fineglass particle deposited body that is a deposition of the fine glassparticles.

Thereafter, the glass particle deposited body thus obtained isdehydrated and sintered in a furnace to obtain a preform.

As described above, according to this embodiment, gases can be suppliedto a plurality of supply targets with high uniformity and highreproducibility.

Fourth Embodiment

A gas branching apparatus according to a fourth embodiment of thepresent invention is described. Note that the same constituentcomponents as those in the gas branching apparatus according to thethird embodiment described above are denoted by the same referencenumerals, and description thereof is omitted or simplified.

In the third embodiment described above, the description is given of, asan example, the case where the opening and closing of the air valvesBVxy are controlled so as to randomly switch two or more times the flowdivider to be used to branch the gas. However, the control of theopening and closing of the air valves BVxy is not limited to the casewhere the control is performed so as to randomly switch two or moretimes the flow divider to be used to branch the gas. For example, theopening and closing of the air valves BVxy may be controlled so as toregularly switch two or more times the flow divider to be used to branchthe gas.

In this embodiment, description is given of the case where opening andclosing of the air valves BVxy are controlled so as to regularly switchtwo or more times the flow divider to be used to branch the gas.

In this case, for example, every time a predetermined time interval forswitching the flow divider to be used to branch the gas passes, the pairof the air valves BV11 and BV12, the pair of the air valves BV21 andBV22, and the pair of the air valves BV31 and BV32 are repeatedly set tothe opened state in this order. Meanwhile, the rest of the pairs otherthan those set to the opened state are set to the closed state. Thus,the flow divider to be used to branch the gas is sequentially andrepeatedly switched in the order of the flow divider 114-1, the flowdivider 114-2, and the flow divider 114-3.

As described above, opening and closing of the air valves BVxy can alsobe controlled so as to regularly switch two or more times the flowdivider to be used to branch the gas. Such regular switching can alsoreduce the influences of gravity and the influences of the variations inmembers or parts. Therefore, according to this embodiment, the gases canbe supplied to the plurality of burners 110-1 to 110-3 with highuniformity while reducing the influences of gravity and the influencesof the variations in members or parts.

Note that, in this case, again, it is preferable that the switching ofthe flow divider to be used to branch the gas is performed such that acumulative time of times when the flow dividers 114-1 to 114-3 are usedto branch the gas is equal thereamong.

Fifth Embodiment

A gas branching apparatus according to a fifth embodiment of the presentinvention is described. Note that the same constituent components asthose in the gas branching apparatus according to the third and fourthembodiments described above are denoted by the same reference numerals,and description thereof is omitted or simplified.

In the third and fourth embodiments, the description is given of, as anexample, the case where the plurality of flow dividers 114-1 to 114-3are vertically arranged. In this case, the array direction of theplurality of gas outlets 114-1 o-1 to 114-1 o-3, 114-2 o-1 to 114-2 o-3,and 114-3 o-1 to 114-3 o-3 is vertical as in the case of thelongitudinal direction of the core material 112. However, the mode ofarranging the plurality of flow dividers 114-1 to 114-3 is not limitedto the vertical arrangement. For example, the plurality of flow dividers114-1 to 114-3 may be horizontally arranged.

In this embodiment, description is given of the case where the pluralityof flow dividers 114-1 to 114-3 are horizontally arranged.

In this case, the array direction of the plurality of gas outlets 114-1o-1 to 114-1 o-3, 114-2 o-1 to 114-2 o-3, and 114-3 o-1 to 114-3 o-3 ishorizontal in the horizontally arranged flow dividers 114-1 to 114-3.

Note that the core material 112 is held such that its longitudinaldirection is vertical as in the case of the third and fourthembodiments.

As described above, in this embodiment where the plurality of flowdividers 114-1 to 114-3 are horizontally arranged, again, the controller124 randomly switches the flow divider to be used to branch the gas, asin the case of the third and fourth embodiments. Thus, the influences ofthe variations in members or parts due to the processing accuracy oraging changes as described above can be reduced. Therefore, according tothis embodiment, the gas can be supplied to the plurality of burners110-1 to 110-3 with high uniformity while reducing the influences of thevariations in members or parts.

The present invention is not limited to the third to fifth embodimentsdescribed above, but various modifications can be made thereto.

For example, in the third to fifth embodiments, the description is givenof, as an example, the case where the gas is branched and supplied intothe three burners 110-1 to 110-3. However, the number of the burners isnot particularly limited as long as two or more burners are provided.Moreover, the description is given of, as an example, the case where thegas branching apparatus 1100 includes the three flow dividers 114-1 to114-3. However, the number of the flow dividers is not particularlylimited as long as two or more flow dividers are provided. It ispreferable, however, that the number of the flow dividers is 10 or lessto prevent the apparatus from becoming complex.

When a gas is branched and supplied into first to N-th (where N is aninteger of 2 or more) burners, a plurality of flow dividers having thesame design are used. The flow dividers each include first to N-th gasoutlets through which the gas is branched and discharged, and aredesigned so as to have an equal branching ratio of the gas to the firstto N-th gas outlets. The first to N-th gas outlets of each of theplurality of flow dividers are located at the different positions suchas vertical positions each other in the flow divider. Via each of pipes,one of the first to N-th gas outlets of each of the plurality of flowdividers is connected to any of the first to N-th burners on aone-to-one basis. The plurality of gas outlets connected to the first toN-th burners, respectively, are located at the different positions suchas vertical positions each other in the flow divider.

When the gas is branched and supplied to the first to N-th burners, thecontroller may switch the flow divider to be used to branch the gas soas to use any one of the plurality of flow dividers for branching of thegas.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case where the burners 110-1 to 110-3 are used asa plurality of supply targets to be supplied with the gas. However, thesupply targets are not limited to the burners. The supply targets may bethose subjected to some kind of processing, such as manufacturing ofproducts and processing on processed products, using the supplied gas.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case where the burners 110-1 to 110-3 as thesupply targets are arranged along the longitudinal direction of the corematerial 112 that is an object. However, the plurality of supply targetsdo not always have to be those arranged along the longitudinal directionof the object.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case using the air valves BVxy. However, insteadof the air valves, various valves can be used, whose opening and closingcan be controlled by the controller 124. For example, electromagneticvalves or the like can be used instead of the air valves.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case where the flow divider to be used to branchthe gas is switched by controlling the opening and closing of the airvalves. A method for switching the flow divider is not limited thereto.Various other methods can be used to switch the flow divider to be usedto branch the gas.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case where the core material 112 is held suchthat the longitudinal direction thereof is vertical. However, the modeof holding the core material 112 is not limited thereto. For example,the core material 112 may be held such that the longitudinal directionthereof is horizontal. In this case, the burners 110-1 to 110-3 can bearranged at equal intervals along the longitudinal direction of the corematerial 112 that is horizontally disposed. Moreover, the flow dividers114-1 to 114-3 can be vertically or horizontally arranged as describedabove.

Moreover, in the third to fifth embodiments, the description is givenof, as an example, the case where the number of the plurality of burners110-1 to 110-3 is the same as the number of the plurality of flowdividers 114-1 to 114-3. However, the numbers thereof do not always haveto be the same. It is preferable, however, that the number of theplurality of burners is the same as the number of the plurality of flowdividers. Thus, the gas outlets at all the positions in the flowdividers can be connected to the respective burners.

Moreover, the third to fifth embodiments are also applicable to the casewhere the branching ratio of the flow divider is not even.

Sixth Embodiment

With reference to FIGS. 5 and 6, description is given of a gas branchingapparatus according to a sixth embodiment of the present invention. FIG.5 is a schematic diagram showing the gas branching apparatus accordingto this embodiment. FIG. 6 is a flowchart showing operations of the gasbranching apparatus according to this embodiment.

First, with reference to FIG. 5, description is given of a configurationof the gas branching apparatus according to this embodiment.

As shown in FIG. 5, a gas branching apparatus 2100 according to thisembodiment branches and supplies a gas into a plurality of burners 210-1to 210-3, which are supply targets to be supplied with the gas. Notethat the following description is given of, as an example, the casewhere the burners 210-1 to 210-3 are burners for manufacturing a fineglass particle deposited body for optical fiber by use of the OVDmethod. Also, while the number of the burners is not particularlylimited as long as two or more burners are provided, the followingdescription is given of, as an example, the case where three burners210-1 to 210-3 are used.

The burners 210-1 to 210-3 are made of quartz glass, for example, whichare manufactured with the same design. Each of the burners 210-1 to210-3 is supplied with a plurality of gases to form a flame andintroduce a raw gas into the flame. The plurality of gases to besupplied to each of the burners 210-1 to 210-3 are, for example,hydrogen (H₂) gas, oxygen (O₂) gas, argon (Ar) gas, and raw gas. The rawgas includes SiC1 ₄ and the like. In the OVD method, for each of theburners 210-1 to 210-3, such gases are used to form an oxyhydrogen flameand the raw gas is introduced into the oxyhydrogen flame. Although flowrates of the respective gases to the burners 210-1 to 210-3 are notparticularly limited, a flow rate of the H₂ gas is, for example, 20000to 40000 sccm. A flow rate of the O₂ gas is, for example, 35000 to 40000sccm. A flow rate of the Ar gas is, for example, 3000 to 5000 sccm. Aflow rate of the raw gas is, for example, 3000 to 10000 sccm.

Note that the following description is given of, as an example, aconfiguration where one of the plurality of gases is supplied to each ofthe burners 210-1 to 210-3. However, a configuration where another gasis supplied to each of the burners 210-1 to 210-3 may also be the sameas the configuration described below.

A long rod-shaped core material 212, onto which flames are blown fromthe burners 210-1 to 210-3, is a material on which fine glass particlesare deposited to be a preform, and is a glass rod, for example. The corematerial 212 is held such that its longitudinal direction is horizontal.Also, the core material 212 is held so as to be rotatable with itscentral axis as a rotation axis. The length of the core material 212 is,for example, but not particularly limited to, several meters, morespecifically, 1 to 2 m, for example.

The burners 210-1 to 210-3 are arranged in the horizontal direction atequal intervals along the longitudinal direction of the long rod-shapedcore material 212. Note that while the description is given of, as anexample, the case where the three burners 210-1 to 210-3 are provided inthis embodiment, the number of burners to be arranged for the corematerial 212 having a length of 1 to 2 m, for example, can be set to 5to 30. Thus, since the burners 210-1 to 210-3 are arranged at equalintervals, a plurality of flames from the burners 210-1 to 210-3 areblown toward the core material 212 at equal intervals.

Moreover, the burners 210-1 to 210-3 are configured to be movable backand forth within a predetermined range along the longitudinal directionof the core material 212. Note that the core material 212 may beconfigured to be movable back and forth along its longitudinaldirection, instead of the burners 210-1 to 210-3 being configured to bemovable back and forth.

The gas branching apparatus 2100 according to this embodiment includes aplurality of flow dividers 214-1 to 214-3 configured to branch a gas tobe supplied to the plurality of burners 210-1 to 210-3. Also, the gasbranching apparatus 2100 according to this embodiment includes a pipingsystem for supplying a gas to the flow dividers 214-1 to 214-3 and apiping system for connecting between the plurality of flow dividers214-1 to 214-3 and the plurality of burners 210-1 to 210-3.

The flow dividers 214-1 to 214-3 are made of metal, for example, andhave different volumes. More specifically, the flow divider 214-1 has asmall volume. The flow divider 214-2 has a medium volume larger than thevolume of the flow divider 214-1. The flow divider 214-3 has a largevolume larger than the volume of the flow divider 214-2. The flowdividers 214-1 to 214-3 are used according to the flow rate of the gasto be branched, as described later.

The flow divider 214-1 includes two gas inlets 214-1 i-1 and 214-1 i-2and a plurality of gas outlets 214-1 o-1 to 214-1 o-3, which are thesame in number as the plurality of burners 210-1 to 210-3. The pluralityof gas outlets 214-1 o-1 to 214-1 o-3 are provided at equal intervals ina certain array direction.

The flow divider 214-2 includes two gas inlets 214-2 i-1 and 214-2 i-2and a plurality of gas outlets 214-2 o-1 to 214-2 o-3, which are thesame in number as the plurality of burners 210-1 to 210-3. The pluralityof gas outlets 214-2 o-1 to 214-2 o-3 are provided at equal intervals ina certain array direction.

The flow divider 214-3 includes two gas inlets 214-3 i-1 and 214-3 i-2and a plurality of gas outlets 214-3 o-1 to 214-3 o-3, which are thesame in number as the plurality of burners 210-1 to 210-3. The pluralityof gas outlets 214-3 o-1 to 214-3 o-3 are provided at equal intervals ina certain array direction.

The flow dividers 214-1 to 214-3 are horizontally arranged. In the flowdividers 214-1 to 214-3 horizontally arranged, the array direction ofthe plurality of gas outlets 214-1 o-1 to 214-1 o-3, 214-2 o-1 to 214-2o-3, and 214-3 o-1 to 214-3 o-3 is horizontal as in the case of thelongitudinal direction of the core material 212.

Note that the volumes of the flow dividers 214-1 to 214-3 are notparticularly limited but can be selected according to gas supplyconditions and the like. The volume of the small-volume flow divider214-1 is, for example, 500 to 1000 cm³. The volume of the medium-volumeflow divider 214-2 is, for example, 1000 to 2000 cm³. The volume of thelarge-volume flow divider 214-3 is, for example, 2000 to 3000 cm³.Moreover, although description is given of the case where the flowdividers 214-1 to 214-3 each include two gas inlets, the number of thegas inlets is not limited to 2. The number of the gas inlets may be oneor two or more, and can be changed as needed according to the gas supplyconditions, the volumes of the flow dividers 214-1 to 214-3, and thelike.

The gas branching apparatus 2100 according to this embodiment includespipes 216-1 and 216-2 for supplying the flow dividers 214-1 to 214-3with the same kind of gas as that to be supplied to the burners 110-1 to110-3. The pipes 216-1 and 216-2 have their upstream ends connected to asupply source (not shown) of the gas to be supplied to the burners 210-1to 210-3. The pipes 216-1 and 216-2 are provided with MFCs 218-1 and218-2, respectively. The MFCs 218-1 and 218-2 enable control of flowrates of gases flowing toward the flow dividers 214-1 to 214-3 throughthe pipes 216-1 and 216-2.

The pipes 216-1 and 216-2 are each branched, at their downstream endside, into a plurality of branch pipes, which are the same in number asthe flow dividers 214-1 to 214-3. More specifically, the pipe 216-1 isbranched into branch pipes 216-1-1 to 216-1-3 at its downstream endside. The pipe 216-2 is branched into branch pipes 216-2-1 to 216-2-3 atits downstream end side.

The branch pipes 216-1-1 and 216-2-1 have their downstream endsconnected to two gas inlets 214-1 i-1 and 214-1 i-2 of the flow divider214-1, respectively. The branch pipes 216-1-2 and 216-2-2 have theirdownstream ends connected to two gas inlets 114-2 i-1 and 214-2 i-2 ofthe flow divider 214-2, respectively. The branch pipes 216-1-3 and216-2-3 have their downstream ends connected to two gas inlets 214-3 i-1and 214-3 i-2 of the flow divider 214-1, respectively.

The branch pipes of the pipes 216-1 and 216-2 are provided withinlet-side air valves for opening and closing the branch pipes,respectively. More specifically, the branch pipes 216-1-1 and 216-2-1are provided with inlet-side air valves AVi11 and AVi12, respectively.The branch pipes 216-1-2 and 216-2-2 are provided with inlet-side airvalves AVi21 and AVi22, respectively. The branch pipes 216-1-3 and216-2-3 are provided with inlet-side air valves AVi31 and AVi32,respectively. Note that, in the following description, these inlet-sideair valves may be described as the inlet-side air valves AVixy (where xis an integer that satisfies 1≤x≤3 and y is 1 or 2). Moreover, theinlet-side air valves may also be simply called air valves.

Moreover, pipes 220-1-1 to 220-1-3 have their upstream ends connected tothe plurality of gas outlets 214-1 o-1 to 214-1 o-3 of the flow divider214-1, respectively. The flow divider 214-1 is designed so as to have anequal branching ratio of the gas to the plurality of gas outlets 214-1o-1 to 214-1 o-3. More specifically, the flow divider 214-1 is designedsuch that the gas introduced into the flow divider 214-1 through thepipes 216-1-1 and 216-2-1 is delivered into the pipes 220-1-1 to 220-1-3with an equal branching ratio through the plurality of gas outlets 214-1o-1 to 214-1 o-3.

The pipes 220-1-1 to 220-1-3 are provided with outlet-side air valvesAVo11, AVo12, and AVo13 for opening and closing the pipes 220-1-1 to220-1-3, respectively. Note that, instead of the outlet-side air valvesAVo11, AVo12, and AVo13, check valves may be provided to prevent the gasfrom flowing back from the downstream side toward the flow divider 214-1that is the upstream side in the pipes 220-1-1 to 220-1-3.

Moreover, pipes 220-2-1 to 220-2-3 have their upstream ends connected tothe plurality of gas outlets 214-2 o-1 to 214-2 o-3 of the flow divider214-2, respectively. The flow divider 214-2 is designed so as to have anequal branching ratio of the gas to the plurality of gas outlets 214-2o-1 to 214-2 o-3. More specifically, the flow divider 214-2 is designedsuch that the gas introduced into the flow divider 214-2 through thepipes 216-1-2 and 216-2-2 is delivered into the pipes 220-2-1 to 220-2-3with an equal branching ratio through the plurality of gas outlets 214-2o-1 to 214-2 o-3.

The pipes 220-2-1 to 220-2-3 are provided with outlet-side air valvesAVo21, AVo22, and AVo23 for opening and closing the pipes 220-2-1 to220-2-3, respectively. Note that, instead of the outlet-side air valvesAVo21, AVo22, and AVo23, check valves may be provided to prevent the gasfrom flowing back from the downstream side toward the flow divider 214-2that is the upstream side in the pipes 220-2-1 to 220-2-3.

Moreover, pipes 220-3-1 to 220-3-3 have their upstream ends connected tothe plurality of gas outlets 214-3 o-1 to 214-3 o-3 of the flow divider214-3, respectively. The flow divider 214-3 is designed so as to have anequal branching ratio of the gas to the plurality of gas outlets 214-3o-1 to 214-3 o-3. More specifically, the flow divider 214-3 is designedsuch that the gas introduced into the flow divider 214-3 through thepipes 216-1-3 and 216-2-3 is delivered into the pipes 220-3-1 to 220-3-3with an equal branching ratio through the plurality of gas outlets 214-3o-1 to 214-3 o-3.

The pipes 220-3-1 to 220-3-3 are provided with outlet-side air valvesAVo31, AVo32, and AVo33 for opening and closing the pipes 220-3-1 to220-3-3, respectively. Note that, instead of the outlet-side air valvesAVo31, AVo32, and AVo33, check valves may be provided to prevent the gasfrom flowing back from the downstream side toward the flow divider 214-3that is the upstream side in the pipes 220-3-1 to 220-3-3.

Note that, in the following description, the above outlet-side airvalves may be described as the outlet-side air valves AVomn (where m isan integer that satisfies 1≤m≤3 and n is an integer that satisfies1≤n≤3). Moreover, the outlet-side air valves may also be simply calledair valves.

The pipes 220-1-1, 220-2-1, and 220-3-1 have their downstream endsconnected in common to an upstream end of a pipe 222-1. The pipes220-1-2, 220-2-2, and 220-3-2 have their downstream ends connected incommon to an upstream end of a pipe 222-2. The pipes 220-1-3, 220-2-3,and 220-3-3 have their downstream ends connected in common to anupstream end of a pipe 222-3.

The pipe 222-1 has its downstream end connected to the burner 210-1, sothat the burner 210-1 is supplied with a gas through the pipe 222-1. Thepipe 222-2 has its downstream end connected to the burner 210-2, so thatthe burner 210-2 is supplied with a gas through the pipe 222-2. The pipe222-3 has its downstream end connected to the burner 210-3, so that theburner 210-3 is supplied with a gas through the pipe 222-3.

Thus, the plurality of gas outlets of each of the plurality of flowdividers 214-1 to 214-3 are connected in 1:1 through the pipes to any ofthe plurality of burners 210-1 to 210-3. More specifically, the gasoutlet 214-1 o-1 of the flow divider 214-1 is connected to the burner210-1 through the pipes 220-1-1 and 222-1. The gas outlet 214-1 o-2 ofthe flow divider 214-1 is connected to the burner 210-2 through thepipes 220-1-2 and 222-2. The gas outlet 214-1 o-3 of the flow divider214-1 is connected to the burner 210-3 through the pipes 220-1-3 and222-3. The gas outlet 214-2 o-1 of the flow divider 214-2 is connectedto the burner 210-1 through the pipes 220-2-1 and 222-1.

The gas outlet 214-2 o-2 of the flow divider 214-2 is connected to theburner 210-2 through the pipes 220-2-2 and 222-2. The gas outlet 214-2o-3 of the flow divider 214-2 is connected to the burner 210-3 throughthe pipes 220-2-3 and 222-3. The gas outlet 214-3 o-1 of the flowdivider 214-3 is connected to the burner 210-1 through the pipes 220-3-1and 222-1. The gas outlet 214-3 o-2 of the flow divider 214-3 isconnected to the burner 210-2 through the pipes 220-3-2 and 222-2. Thegas outlet 214-3 o-3 of the flow divider 214-3 is connected to theburner 210-3 through the pipes 220-3-3 and 222-3.

The gas branching apparatus 2100 according to this embodiment furtherincludes a controller 224 configured to control opening and closing ofthe inlet-side air valves AVixy and the outlet-side air valves AVomn.The controller 224 includes a CPU (not shown) configured to executevarious kinds of processing such as calculation, control, anddetermination. The controller 224 also includes a ROM (not shown)configured to store various control programs to be executed by the CPU,a database to be referred to by the CPU, and the like. The controller224 further includes a RAM (not shown) configured to temporarily storedata that is being processed by the CPU, input data, and the like.

The controller 224 controls opening and closing of the inlet-side airvalves AVixy and the outlet-side air valves AVomn so as to switch theflow divider to be used to branch the gas to any of the flow dividers214-1 to 214-3 during manufacturing of the fine glass particle depositedbody using the flames from the burners 210-1 to 210-3. As to switchingof the flow divider to be used, the controller 224 controls opening andclosing of the inlet-side air valves AVi11 and AVi12 and the outlet-sideair valves AVo11, AVo12, and AVo13 in synchronization with the flowdivider 214-1. The controller 224 controls opening and closing of theinlet-side air valves AVi21 and AVi22 and the outlet-side air valvesAVo21, AVo22, and AVo23 in synchronization with the flow divider 214-2.The controller 224 controls opening and closing of the inlet-side airvalves AVi31 and AVi32 and the outlet-side air valves AVo31, AVo32, andAVo33 in synchronization with the flow divider 214-3. Moreover, thecontroller 224 sets any one of the groups of the air valves to becontrolled in synchronization, including the group of the air valvesAVi11, AVi12, AVo11, AVo12, and AVo13, the group of the air valvesAVi21, AVi22, AVo21, AVo22, and AVo23, and the group of the air valvesAVi31, AVi32, AVo31, AVo32, and AVo33 to the opened state, and the restof the groups to the closed state.

The controller 224 acquires a flow rate of the gas to be branched fromthe MFCs 218-1 and 218-2, and executes the switching of the flow dividerdescribed above according to the flow rate of the gas to be branched.More specifically, the controller 224 switches the flow divider to beused to branch the gas to the small-volume flow divider 214-1 when theflow rate of the gas to be branched is the low flow rate. The controller224 switches the flow divider to be used to branch the gas to themedium-volume flow divider 214-2 when the flow rate of the gas is themedium flow rate, which is higher than the low flow rate. The controller224 switches the flow divider to be used to branch the gas to thelarge-volume flow divider 214-3 when the flow rate of the gas is thehigh flow rate, which is higher than the medium flow rate.

Note that the flow rates of the gas using the flow dividers 214-1 to214-3 are not particularly limited. For example, when the flow rate ofthe gas to be branched is the low flow rate of 3000 to 5000 sccm, thesmall-volume flow divider 214-1 having a volume of 500 to 1000 cm³ canbe used. When the flow rate of the gas to be branched is the medium flowrate of 5000 to 8000 sccm, the medium-volume flow divider 214-2 having avolume of 1000 to 2000 cm³ can be used. When the flow rate of the gas tobe branched is the high flow rate of 8000 to 10000 sccm, thelarge-volume flow divider 214-3 having a volume of 2000 to 3000 cm³ canbe used.

The gas is supplied to the respective burners 210-1 to 210-3 whilechanging the flow rate with the passage of time from the start ofmanufacturing of one fine glass particle deposited body to the end ofmanufacturing. For example, from the start to the end of manufacturing,the gas is supplied to the burners 210-1 to 210-3 such that the flowrate is gradually increased over time. Thus, the flow rate of the gas tobe branched is also changed over time, for example, gradually increased.In the gas branching apparatus 2100 according to this embodiment, theflow divider to be used to branch the gas is switched to any of the flowdividers 214-1 to 214-3 according to the flow rate of the gas, which ischanged in such a manner. Note that the mode in which the flow rate ofthe gas is changed is not particularly limited. Besides the mode inwhich the flow rate is gradually increased over time, for example, amode in which the flow rate is gradually decreased over time, a mode inwhich the flow rate is gradually increased or gradually decreased overtime, a mode in which the flow rate is increased and decreased overtime, or a combination of these modes may be adopted.

As for manufacturing of the fine glass particle deposited body foroptical fiber, the flow rate of the gas to be supplied to the pluralityof burners may be changed. Thus, the flow rate of the gas to be branchedby the flow divider is also changed. However, when the volume of theflow divider is not appropriate, i.e., too small or too large, withrespect to the flow rate of the gas, inconvenience occurs, such asdifficulty with equal branching.

To be more specific, first, when the gas to be branched has a high flowrate, influences of dynamic pressure are increased if the volume of theflow divider is too small. Therefore, a flow divider having a structurein which an outlet side flow path is narrowed generally results indifficulty with equal branching. On the other hand, when the gas to bebranched has a low flow rate, it takes time before the pressure insidethe flow divider is equalized if the volume of the flow divider is toolarge. This delays a change in flow rate on the outlet side, makingequal branching difficult.

For this reason, when the flow rate of the gas to be branched ischanged, such a flow rate may make the branching ratio of the flowdivider unstable. Such an unstable branching ratio of the flow dividermakes it difficult to supply the gas to the plurality of burners withhigh uniformity. As a result, uniformity and stability of the fine glassparticle deposited body in its longitudinal direction, which ismanufactured along the longitudinal direction of the core material, maybe impaired.

To counter this, in the gas branching apparatus 2100 according to thisembodiment, the controller 224 switches the flow divider to be used tobranch the gas among the flow dividers 214-1 to 214-3 having differentvolumes according to the flow rate of the gas to be branched. Byswitching the flow divider according to the flow rate of the gas to bebranched as described above, a more appropriate flow divider can be usedaccording to the flow rate of the gas to be branched. Thus, the gas canbe stably branched and supplied to the burners 210-1 to 210-3 with highuniformity while reducing the influences of the flow rate. Therefore,according to this embodiment, a fine glass particle deposited bodyexcellent in uniformity and stability in the longitudinal direction canbe manufactured.

Next, with reference to FIG. 6, description is further given ofoperations of the gas branching apparatus 2100 according to thisembodiment.

Before the gas branching apparatus 2100 starts its operation, theinlet-side air valves AVixy and the outlet-side air valves AVomn are allset in the closed state.

First, the gas branching apparatus 2100 starts its operation, therebyintroducing a gas into the flow dividers 214-1 to 214-3 through thepipes 216-1 and 216-2. During the introduction of the gas through thepipes 216-1 and 216-2, the MFCs 218-1 and 218-2 control the flow ratesof the gases flowing through the pipes 216-1 and 216-2, respectively.

The controller 224 acquires the flow rate of the gas to be branched fromthe MFCs 218-1 and 218-2 (Step S211).

Next, the controller 224 determines whether or not the flow rateacquired from the MFCs 218-1 and 218-2 is not more than a flow ratevalue f1 that is an upper limit for the use of the small-volume flowdivider 214-1 (Step S212). When the flow rate is not more than the flowrate value f1 (Step S212, YES), the controller 224 sets the group of theair valves AVi11, AVi12, AVo11, AVo12, and AVo13 to the opened state. Atthe same time, the controller 224 sets the group of the air valvesAVi21, AVi22, AVo21, AVo22, and AVo23 and the group of the air valvesAVi31, AVi32, AVo31, AVo32, and AVo33 to the closed state. Thus, thesmall-volume flow divider 214-1 is set as the flow divider to be used tobranch the gas (Step S213).

On the other hand, when the flow rate is more than the flow rate valuef1 (Step S212, NO), the controller 224 determines whether or not theflow rate acquired from the MFCs 218-1 and 218-2 is not more than a flowrate value f2 that is an upper limit for the use of the medium-volumeflow divider 214-2 (Step S214). Note that the flow rate value f2 islarger than the flow rate value f1. When the flow rate is not more thanthe flow rate value f2 (Step S214, YES), the controller 224 sets thegroup of the air valves AVi21, AVi22, AVo21, AVo22, and AVo23 to theopened state. At the same time, the controller 224 sets the group of theair valves AVi11, AVi12, AVo11, AVo12, and AVo13 and the group of theair valves AVi31, AVi32, AVo31, AVo32, and AVo33 to the closed state.Thus, the medium-volume flow divider 214-2 is set as the flow divider tobe used to branch the gas (Step S215).

On the other hand, when the flow rate is more than the flow rate valuef2 (Step S214, NO), the controller 224 sets the group of the air valvesAVi31, AVi32, AVo31, AVo32, and AVo33 to the opened state. At the sametime, the controller 224 sets the group of the air valves AVi11, AVi12,AVo11, AVo12, and AVo13 and the group of the air valves AVi21, AVi22,AVo21, AVo22, and AVo23 to the closed state. Thus, the large-volume flowdivider 214-3 is set as the flow divider to be used to branch the gas(Step S216).

After setting the flow divider to be used to branch the gas according tothe flow rate of the gas as described above, the gas is branched by theset flow divider and supplied to the plurality of burners 210-1 to210-3, respectively (Step S217). Note that other gases used tomanufacture a fine glass particle deposited body are similarly suppliedto the plurality of burners 210-1 to 210-3.

In the respective burners 210-1 to 210-3 supplied with the gases asdescribed above, flames are formed using a fuel gas among the gasessupplied, and a raw gas among the gases supplied is introduced into theflames. Thus, the flames containing the raw material are blown onto thecore material 112 rotated with its central axis as a rotation axis.Accordingly, fine glass particles to be a preform of optical fiber aresequentially deposited on the core material 212. Note that, in themeantime, the plurality of burners 210-1 to 210-3 may be moved back andforth along the longitudinal direction of the core material 112.

During the deposition of the fine glass particles on the core material212 as described above, the deposition weight of the fine glassparticles deposited on the core material 212 is monitored, and it isdetermined based on the monitored deposition weight whether or not toterminate the deposition of the fine glass particles (Step S218).

When the deposition weight of the fine glass particles is less than apredetermined weight and the deposition is continued rather than beingterminated (Step S218, NO), the processing returns to Step S211 tocontinue the deposition of the fine glass particles by supplying therespective gases while switching the flow divider according to the flowrate of the gas as described above.

On the other hand, when the deposition weight of the fine glassparticles is the predetermined weight and thus the deposition is to beterminated (Step S218, YES), the controller 124 sets all the inlet-sideair valves AVixy and the outlet-side air valves AVomn in the closedstate (Step S219). Thus, the deposition of the fine glass particles onthe core material 212 is terminated to obtain a fine glass particledeposited body that is a deposition of the glass particles.

Thereafter, the fine glass particle deposited body thus obtained isdehydrated and sintered in a furnace to obtain a preform.

As described above, according to this embodiment, gases can be suppliedto a plurality of supply targets with high uniformity.

Note that the above description is given of the case where the flowdividers 214-1 to 214-3 are switched thereamong during the manufacturingof one fine glass particle deposited body. Meanwhile, in the case ofmanufacturing different kinds of fine glass particle deposited bodiesdifferent in size, material composition, and the like, the flow rates ofthe gases to be supplied to the burners may also be different, and theflow rates of the gases to be branched may also be different. In such acase of manufacturing different kinds of fine glass particle depositedbodies different in size and the like, the flow dividers 214-1 to 214-3to be used to branch the gas can also be switched and used according tothe kind of the fine glass particle deposited body. Thus, in the case ofmanufacturing different kinds of fine glass particle deposited bodies,again, stable branching of the gas can be realized during manufacturingof the respective fine glass particle deposited bodies.

Seventh Embodiment

With reference to FIG. 7, description is given of a gas branchingapparatus according to a seventh embodiment of the present invention.Note that the same constituent components as those in the gas branchingapparatus according to the sixth embodiment described above are denotedby the same reference numerals, and description thereof is omitted orsimplified.

In the sixth embodiment, the description is given of, as an example, thecase where the plurality of flow dividers 214-1 to 214-3 havingdifferent volumes are used. However, the plurality of flow dividers214-1 to 214-3 do not always have to be used if the volume of the flowdivider to be used to branch the gas can be changed. More specifically,the use of a volume-variable flow divider can realize stable branchingof the gas while reducing the influences of the flow rate, as in thecase of using the plurality of flow dividers 214-1 to 214-3.

In this embodiment, description is given of the case using a singlevolume-variable flow divider instead of the plurality of flow dividers214-1 to 214-3 having different volumes.

As shown in FIG. 7, a gas branching apparatus 2200 according to thisembodiment includes a volume-variable flow divider 226 configured tobranch a gas to be supplied to a plurality of burners 210-1 to 210-3.Also, the gas branching apparatus 2200 according to this embodimentincludes a piping system for supplying the gas to the flow divider 226and a piping system for connecting between the flow divider 226 and theplurality of burners 210-1 to 210-3.

The flow divider 226 is made of metal, for example, and has a volumevarying mechanism capable of changing its volume. A configuration of thevolume varying mechanism is not particularly limited as long as thevolume of the flow divider 226 can be changed. Note that the volume ofthe volume-variable flow divider 226 is controlled by a controller 228.

The flow divider 226 includes two gas inlets 226 i-1 and 226 i-2 and aplurality of gas outlets 226 o-1 to 2260-3, which are the same in numberas the plurality of burners 210-1 to 210-3. The plurality of gas outlets226 o-1 to 226 o-3 are provided at equal intervals in a certain arraydirection. The flow divider 226 is disposed such that the arraydirection of the plurality of gas outlets 226 o-1 to 226 o-3 ishorizontal as in the case of the longitudinal direction of the corematerial 212, for example.

Note that the volume variable range of the flow divider 226 is notparticularly limited, and can be selected according to gas supplyconditions and the like. For example, the volume of the flow divider 226can be changed within the range of 500 to 3000 cm³. Moreover, while thedescription is given of the case where the flow divider 226 includes thetwo gas inlets 226 i-1 and 226 i-2, the number of the gas inlets is notlimited to 2. The number of the gas inlets may be one or two or more,and can be changed as needed according to the volume variable range ofthe flow divider 226, and the like.

The gas branching apparatus 2200 according to this embodiment includespipes 216-1 and 216-2 for supplying the flow divider 226 with the samekind of gas as that to be supplied to the burners 210-1 to 210-3. Thepipes 216-1 and 216-2 have their upstream ends connected to a supplysource (not shown) of the gas to be supplied to the burners 210-1 to210-3. The pipes 216-1 and 216-2 are provided with MFCs 218-1 and 218-2,respectively. The MFCs 218-1 and 218-2 enable control of flow rates ofgases flowing toward the flow dividers 214-1 to 214-3 through the pipes216-1 and 216-2.

The pipes 216-1 and 216-2 have their downstream ends connected to twogas inlets 226 i-1 and 226 i-2 of the flow divider 226, respectively.

Moreover, the pipes 220-1 to 220-3 have their upstream ends connected tothe plurality of gas outlets 226 o-1 to 2260-3 of the flow divider 226,respectively. The flow divider 226 is designed so as to have an equalbranching ratio of the gas to the plurality of gas outlets 226 o-1 to226 o-3 within the volume variable range. More specifically, the flowdivider 226 is designed such that the gas introduced into the flowdivider 226 through the pipes 216-1 and 216-2 is delivered into thepipes 220-1 to 220-3 with an equal branching ratio through the pluralityof gas outlets 226 o-1 to 2260-3.

The pipes 220-1 to 220-3 are provided with air valves AV1 to AV3 foropening and closing the pipes 220-1 to 220-3, respectively.

The pipe 220-1 has its downstream end connected to the burner 210-1, sothat the burner 210-1 is supplied with a gas through the pipe 220-1. Thepipe 220-2 has its downstream end connected to the burner 210-2, so thatthe burner 210-2 is supplied with a gas through the pipe 220-2. The pipe220-3 has its downstream end connected to the burner 210-3, so that theburner 210-3 is supplied with a gas through the pipe 220-3.

The gas branching apparatus 2200 according to this embodiment furtherincludes the controller 228 configured to control opening and closing ofthe air valves AV1 to AV3 and to control the volume of thevolume-variable flow divider 226. The controller 228 includes a CPU (notshown) configured to execute various kinds of processing such ascalculation, control, and determination. The controller 228 alsoincludes a ROM (not shown) configured to store various control programsto be executed by the CPU, a database to be referred to by the CPU, andthe like. The controller 228 further includes a RAM (not shown)configured to temporarily store data that is being processed by the CPU,input data, and the like.

During manufacturing of a fine glass particle deposited body usingflames from the burners 210-1 to 210-3, the controller 228 sets the airvalves AV1 to AV3 in the opened state and controls the volume of thevolume-variable flow divider 226 according to the flow rate of the gasto be branched by the flow divider 226.

The controller 228 acquires a flow rate of the gas to be branched fromthe MFCs 218-1 and 218-2 to control the volume of the flow divider 226according to the flow rate of the gas to be branched. More specifically,the controller 228 sets the volume of the flow divider 226 to arelatively small value when the flow rate of the gas to be branched isrelatively low. On the other hand, the controller 228 sets the volume ofthe flow divider 226 to a relatively large value when the flow rate ofthe gas to be branched is relatively high.

Note that the volume range of the flow divider 226 set by the controller228 is not particularly limited. For example, when the flow rate of thegas is the low flow rate of 3000 to 5000 sccm, the volume of the flowdivider 226 can be set to a small volume value of 500 to 1000 cm³. Whenthe flow rate of the gas is the medium flow rate of 5000 to 8000 sccm,the volume of the flow divider 226 can be set to a medium volume valueof 1000 to 2000 cm³. When the flow rate of the gas is the high flow rateof 8000 to 10000 sccm, the volume of the flow divider 226 can be set toa large volume value of 2000 to 3000 cm³.

By changing the volume of the flow divider 226 according to the flowrate of the gas to be branched as described above, the volume of theflow divider 226 can be set to a more appropriate value according to theflow rate of the gas to be branched. Thus, the gas can be stablybranched and supplied to the burners 210-1 to 210-3 with high uniformitywhile reducing the influences of the flow rate, as in the case of thesixth embodiment. Therefore, according to this embodiment, a fine glassparticle deposited body excellent in uniformity and stability in thelongitudinal direction can be manufactured.

The present invention is not limited to the sixth and seventhembodiments described above, but various modifications can be madethereto.

For example, in the sixth and seventh embodiments, the description isgiven of, as an example, the case where the gas is branched and suppliedinto the three burners 210-1 to 210-3. However, the number of theburners is not particularly limited as long as two or more burners areprovided. Moreover, the description is given of, as an example, the casewhere the gas branching apparatus 2100 includes the three flow dividers214-1 to 214-3 having different volumes. However, the number of the flowdividers having different volumes is not particularly limited as long astwo or more flow dividers are provided. It is preferable, however, thatthe number of the flow dividers is 10 or less to prevent the apparatusfrom becoming complex.

When a gas is branched and supplied into first to N-th (where N is aninteger of 2 or more) burners, a plurality of flow dividers are used.The flow dividers each include first to N-th gas outlets through whichthe gas is branched and discharged, and are designed so as to have anequal branching ratio of the gas to the first to N-th gas outlets. Theplurality of flow dividers have different volumes each other. The firstto N-th gas outlets of the plurality of flow dividers are connected in1:1 through a plurality of pipes to any of the first to N-th burners.

When the gas is branched and supplied to the first to N-th burnersdescribed above, the controller may switch the flow divider to be usedto branch the gas so as to use any one of the plurality of flow dividersfor branching of the gas according to the flow rate of the gas.

Moreover, instead of the plurality of flow dividers, a volume-variableflow divider can also be used. The volume-variable flow divider includesfirst to N-th gas outlets through which the gas is branched anddischarged, and is designed so as to have an equal branching ratio ofthe gas to the first to N-th gas outlets. The first to N-th gas outletsof the volume-variable flow divider are connected in 1:1 through aplurality of pipes to any of the first to N-th burners.

When the volume-variable flow divider described above is used, thecontroller may control the volume of the flow divider according to theflow rate of the gas.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case where the burners 210-1 to 210-3 are used asa plurality of supply targets to be supplied with the gas. However, thesupply targets are not limited to the burners. The supply targets may bethose subjected to some kind of processing, such as manufacturing ofproducts and processing on processed products, using the supplied gas.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case where the burners 210-1 to 210-3 as thesupply targets are arranged along the longitudinal direction of the corematerial 212 that is the object. However, the plurality of supplytargets do not always have to be those arranged along the longitudinaldirection of the object.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case using the air valves AVixy, AVomn, and AV1to AV3. However, instead of the air valves, various valves can be used,whose opening and closing can be controlled by the controllers 224 and228. For example, electromagnetic valves or the like can be used insteadof the air valves.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case where the flow divider to be used to branchthe gas is switched by controlling the opening and closing of the airvalves. A method for switching the flow divider is not limited thereto.Various other methods can be used to switch the flow divider to be usedto branch the gas.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case where the core material 212 is held suchthat the longitudinal direction thereof is horizontal. However, the modeof holding the core material 212 is not limited thereto. For example,the core material 212 may be held such that the longitudinal directionthereof is vertical. In this case, the burners 210-1 to 210-3 arearranged at equal intervals along the longitudinal direction of the corematerial 212 that is vertically disposed. Moreover, the flow dividers214-1 to 214-3 may be horizontally arranged as described above, or maybe vertically arranged.

Moreover, in the sixth and seventh embodiments, the description is givenof, as an example, the case where the number of the plurality of burners210-1 to 210-3 is the same as the number of the plurality of flowdividers 214-1 to 214-3. However, the numbers thereof do not always haveto be the same. The number of the plurality of flow dividers havingdifferent volumes can be set according to the flow rate range of the gasto be branched.

Moreover, the sixth and seventh embodiments are also applicable to thecase where the branching ratio of the flow divider is not even.

What is claimed is:
 1. A gas branching apparatus that branches andsupplies a gas to first to N-th (where N is an integer of 2 or more)supply targets, comprising: a plurality of flow dividers each includingfirst to N-th gas outlets through which the gas is branched anddischarged, the flow dividers having different volumes; and a pluralityof pipes connecting one of the first to N-th gas outlets of each of theplurality of flow dividers to any of the first to N-th supply targets ona one-to-one basis.
 2. The gas branching apparatus according to claim 1,further comprising: a controller configured to switch between the flowdividers to be used to branch the gas, according to a flow rate of thegas, so as to use any one of the plurality of flow dividers forbranching of the gas.
 3. The gas branching apparatus according to claim1, wherein the flow divider is designed so as to have an equal branchingratio of the gas to the first to N-th gas outlets.
 4. The gas branchingapparatus according to claim 1, wherein the first to N-th supply targetsare arranged along a longitudinal direction of a long object.
 5. Amethod for manufacturing a fine glass particle deposited body using thegas branching apparatus according to claim
 1. 6. A gas branchingapparatus that branches and supplies a gas to first to N-th (where N isan integer of 2 or more) supply targets, comprising: a volume-variableflow divider including first to N-th gas outlets through which the gasis branched and discharged; and a plurality of pipes connecting one ofthe first to N-th gas outlets of the flow divider to any of the first toN-th supply targets on a one-to-one basis.
 7. The gas branchingapparatus according to claim 6, further comprising: a controllerconfigured to control a volume of the flow divider according to a flowrate of the gas.
 8. The gas branching apparatus according to claim 6,wherein the flow divider is designed so as to have an equal branchingratio of the gas to the first to N-th gas outlets.
 9. The gas branchingapparatus according to claim 6, wherein the first to N-th supply targetsare arranged along a longitudinal direction of a long object.
 10. Amethod for manufacturing a fine glass particle deposited body using thegas branching apparatus according to claim 6.